Method of viewing and controlling balance of the vertebral column

ABSTRACT

The invention relates to a method of viewing and controlling the balance of a vertebral column of which one spinal segment is corrected by way of conventional spinal instrumentation. The invention method consists of: determining and calculating the relative three-dimensional position of the upper (UEV) and lower (LEV) end instrumented vertebrae of the corrected spinal segment; determining and calculating the position of the spinal segments which are located above and below the spinal segment corrected by the spinal instrumentation, according to the relative three-dimensional position of the upper (UEV) and lower (LEV) end instrumented vertebrae and viewing the front and side projection of the balance or imbalance of the vertebral column.

The present invention relates to a method of viewing and controlling thebalance of a vertebral column of a patient.

The viewing and controlling method according to the present invention ismore particularly designed for viewing and controlling the balance ofthe vertebral column of a patient during an operation on a spinalsegment corrected by means of conventional spinal instrumentation.

The osteosynthesis instrumentation or equipment known to date aregenerally comprised of bone anchoring screws, connectors fixed by thescrews on the vertebral body of each vertebra and connection rodsinterconnecting the connectors. Sometimes, the connection rods aredeformed by the surgeon so as to be able to reestablish the curvature ofthe spinal segment to be corrected.

The idea of balance of the vertebral column is rather complex and ischaracterized by different parameters depending on the clinicalapproach.

Most of the time surgeons evaluate spinal balance both clinically and byradiological photography.

In the latter case, two large-size (30 cm×90 cm) radiographical imagesare taken, one allowing the side of the patient's vertebral column to beviewed and the other the front.

Overall, it is considered that the frontal balance of the vertebralcolumn of the patient is obtained from the moment where the firstthoracic vertebra (T1) is centered with comparison to the sacrum.

As regards sagittal balance, it is considered to be obtained from themoment where the external auditory canals are situated vertically fromthe femoral heads.

When surgical intervention in the vertebral column is necessary, thesimple act of interfusing the vertebrae through instrumentation maycause post-operative balance problems to the patient.

The objective of the surgeon is clearly to first reduce the curvature ofthe spine in the case of spinal deformation and/or to attach a zone thatwill be instrumented.

Subsequently, the surgeon must make sure that the instrumented zoneallows the patient to gain or regain his balance after the operation,when he will take a standing position.

Thus, during the operation, the surgeons attempt to evaluate a possiblepost-operative balance or imbalance in the patient.

Currently surgeons have no system at their disposal that allows them toknow if the instrumented level is going to permit the post-operativebalance of the patient.

Surgeons thus use a single visual assessment of the instrumented segmentin the operative field. Some use a radiographic means (two Rx front+sideimages) that allows them to see a larger view of the vertebral column(from the femoral heads to the cervical vertebrae).

The surgeons may then assess not only the instrumented segment but alsothe segments overlying and underlying the instrumentation in the frontaland sagittal planes.

Unfortunately, these radiographs are performed on the patient who islying down on the operating table, and consequently may notsystematically predict the behavior of the operated vertebral columnwhen the patient stands up after surgery.

The problem consists in that the patient is recumbent on the operatingtable, and only the vertebrae that will be fused are cleared by aconventional posterior surgical approach.

The surgeon instruments these vertebrae, and fuses the same, but may notbe able to assess the consequence of this surgical act on the underlyingand overlying segments that clearly are adapted to the new geometry thatthe surgeon gives to the segment that he instruments.

It is noted that in each instrumentation there exists an upper endinstrumented vertebrae (UEV) and a lower end instrumented vertebrae(LEV) that are respectively connected naturally to the vertebrae of thenon-instrumented vertebral column, that are located above and below theinstrumentation.

It is the orientation of the upper end-plate of the first instrumentedvertebra (UEV) compared to the lower end-plate of the last instrumentedvertebra (LEV) that will define the adaptation behavior of theunderlying and overlying segment.

Consequently, it is the relative position of the two instrumentedvertebrae ends that will determine the geometry of the overlying andunderlying segments.

The instrumented segment is transformed into a large vertebra whose“edges” will determine the adaptation behavior of the overlying andunderlying segments and thus determine the postoperative balance orimbalance of the patient in a standing position.

The object of the method according to the present invention is todetermine the balance of the vertebral column by focusing on the twovertebrae extremes (UEV and LEV).

The method according to the present invention allows the virtual columnof the patient in a standing position after an operation to be seen on acontrol screen.

For that, measurements must be -taken on the end instrumented vertebrae(UEV and LEV).

Measurements taken only on these vertebrae will allow the measuringtime, which is always too long in these often tedious operations, to belimited.

From the measurements taken on these end instrumented vertebrae,calculation algorithms will allow the balance possibilities of thestanding patient after surgery to be projected on the preoperativeradiographs of the patient.

Thus, the present invention provides a method of viewing and controllingthe balance of the vertebral column wherein one spinal segment iscorrected by means of conventional spinal instrumentation, characterizedin that it consists of:

-   -   determining and calculating the relative three-dimensional        position of the upper (UEV) and lower (LEV) end instrumented        vertebrae of the corrected spinal segment through anatomical        points or contours identified or digitalized on the radiographs        of the patient to be treated,    -   determining and calculating the position of the spinal segments        located above and below the spinal segment corrected by the        spinal instrumentation, according to the relative        three-dimensional position of the upper (UEV) and lower (LEV)        end instrumented vertebrae, through anatomical points or        contours identified or digitalized on the radiographs of the        patient to be treated,    -   and viewing the balance or imbalance of the vertebral column (1)        in the vertical position and in front and side projection.

According to an embodiment of the present invention, the relativethree-dimensional position of the upper (UEV) and lower (LEV) endinstrumented vertebrae of the corrected spinal segment is obtained froma first reconstruction in a three-dimensional visual space of thegeometry of the external envelope or contour of the upper (UEV) andlower (LEV) end instrumented vertebrae and a second reconstruction in athree-dimensional visual space of the surface of the neural arch of the(UEV) and lower (LEV) end instrumented vertebrae.

According to an embodiment of the present invention, the first andsecond reconstruction steps in a three-dimensional visual space allowthe relative position of the upper (UEV) and lower (LEV) endinstrumented vertebrae of the corrected spinal segment to be determinedin a three-dimensional visual space.

According to an embodiment of the present invention, the method ofviewing and controlling consists in that the upper (UEV) and lower (LEV)end instrumented vertebrae of the corrected spinal segment are projectedonto front and side radiographs of the patient to be treated.

According to an embodiment of the present invention, the method ofviewing and controlling consists in that the front and side projectionof the upper (UEV) and lower (LEV) end instrumented vertebrae of thecorrected spinal segment allows the position on the front and sideradiographs of the spinal segments located above and below the correctedspinal segment to be determined, and to view the appearance of thereconstructed vertebral column on the front and side radiographs.

According to an embodiment of the present invention, the method ofviewing and controlling consists of identifying or digitalizing at leastfour points delimiting a rectangle reproducing the vertebral body foreach vertebra of the vertebral column.

According to an embodiment of the present invention, the method ofviewing and controlling consists of identifying or digitalizing thepoints that correspond to the radiological indicators utilized, todefine the balance of the head of the patient compared to the pelvis.

According to an embodiment of the present invention, the method ofviewing and controlling consists of identifying or digitalizing at leastten points of the head allowing the external contour of the head to bemarked.

According to an embodiment of the present invention, the method ofviewing and controlling consists of identifying or digitalizing for thepelvis at least the anatomical points defining the center of eachfemoral head and the sacral plate.

According to an embodiment of the present invention, the method ofviewing and controlling consists of identifying or digitalizing at leastfive points of the pelvis wherein one is for each femoral head and atleast three are for the sacrum, in order to form a triangle.

According to an embodiment of the present invention, the method ofviewing and controlling consists of embedding the digitalized points inthe radiographs of the patient.

According to an embodiment of the present invention, the method ofviewing and controlling consists of reconstructing in three dimensionsthe geometric form of the upper (UEV) and lower (LEV) end instrumentedvertebrae from the sagittal and frontal radiographs of the patient.

According to an embodiment of the present invention, the method ofviewing and controlling consists of determining the linear and angulargeometric position of the lower (LEV) end instrumented vertebrae,reconstructed with relation to the front and side radiographs.

According to an embodiment of the present invention, the method ofviewing and controlling consists of projecting the upper (UEV) and lower(LEV) end instrumented vertebrae onto the front and side radiographs.

According to an embodiment of the present invention, the method ofviewing and controlling consists of embedding the projection of theupper (UEV) and lower (LEV) end instrumented vertebrae, with relation toone another, in the radiographs, by registration of the projection ofthe lower end instrumented vertebra (LEV).

The characteristics and advantages of the present invention will beshown in detail in the following description of the particularembodiments in a non-limiting manner with relation to the appendedfigures.

FIG. 1 represents a sagittal radiograph of a standing patient, on whichthe anatomical points are digitalized to identify the pelvis and thefemoral heads.

FIG. 2 illustrates a sagittal radiograph of a standing patientin-cervical flexion, on which the anatomical points are digitalized toidentify the head, the vertebrae overlying the instrumentation and theupper end instrumented vertebrae (UEV).

FIG. 3 shows a sagittal radiograph of a standing patient in cervicalflexion, on which the anatomical points are digitalized to identify thehead, the vertebrae overlying the instrumentation and the upper endinstrumented vertebrae (UEV).

FIG. 4 represents a sagittal radiograph of a seated patient in lumbarflexion, on which the anatomical points are digitalized to identify thepelvis, the vertebrae underlying the instrumentation and the lower endinstrumented vertebrae (LEV).

FIG. 5 represents a sagittal radiograph of a seated patient in lumbarextension, on which the anatomical points are digitalized to identifythe pelvis, the vertebrae underlying the instrumentation and the lowerend instrumented vertebrae (LEV).

FIG. 6 illustrates a frontal radiograph of a standing patient, on whichthe anatomical points are digitalized to identify the pelvis and thefemoral heads.

FIG. 7 shows a frontal radiograph of a patient who is lying down inlateral inflexion to the left, on which the anatomical points aredigitalized to identify the head, the vertebrae overlying and underlyingthe instrumentation, the upper (UEV) and lower (LEV) end instrumentedvertebrae, the pelvis and the femoral heads.

FIG. 8 represents a frontal radiograph of a patient who is lying down inlateral inflexion to the right, on which the anatomical points aredigitalized to identify the head, the vertebrae underlying and overlyingthe instrumentation, the upper (UEV) and lower (LEV) end instrumentedvertebrae, the pelvis and the femoral heads.

FIG. 9 illustrates the radiograph of FIG. 1 in which the digitalizedanatomical points have been embedded in the radiographs of FIGS. 4 and5, this after mapping the scales and adjustment with relation to thepelvis.

FIG. 10 shows the radiograph of FIG. 6 in which the digitalizedanatomical points have been embedded in the radiographs of FIGS. 7 and8, (only those representing the pelvis, the vertebrae underlying theinstrumentation, and the lower (LEV) end instrumented vertebrae), aftermapping the scales and adjustment with relation to the pelvis.

FIG. 11 illustrates the radiograph of FIG. 9 in which the projection ofthe upper (UEV) and lower (LEV) end instrumented vertebrae has beenembedded by registration of the lower end instrumented vertebrae (LEV).

FIG. 12 shows the radiograph of FIG. 10 in which the projection of theupper (UEV) and lower (LEV) end instrumented vertebrae has been embeddedby registration of the lower end instrumented vertebrae (LEV).

FIG. 13 represents the radiograph of FIG. 11 in which the digitalizedpoints have been embedded in the radiograph of FIGS. 2 and 3 (head,overlying vertebrae and upper end instrumented vertebrae (UEV)), byregistration of the upper end instrumented vertebrae (UEV).

FIG. 14 illustrates the radiograph of FIG. 12 in which the digitalizedpoints have been embedded in the radiograph of FIGS. 7 and 8 (head,overlying vertebrae and upper end instrumented vertebrae (UEV)), byregistration of the upper end instrumented vertebrae (UEV)).

First Step of the Method

The first step of the method is to identify or digitalize the anatomicalpoints or contours on the radiographs of the patient to be treated.

Thus for each vertebra 2 of the vertebral column 1, it is necessary toidentify at least four points. These latter delimit a rectanglereproducing the vertebral body.

For the head 3, it is necessary to identify the anatomical points thatusually correspond to the radiological indicators utilized for definingthe balance of the head 3 of the patient with relation to the pelvis 4.

For the head 3, it is necessary to identify in a non-limiting manner, atleast ten points that allow the external contour of the head to bemarked.

For the pelvis 4, it is necessary to identify at least the anatomicalpoints defining the center of each femoral head 5 and the sacrum 6.

For the pelvis 4, it is necessary to identify at least five pointswherein one is for each femoral head 5 and at least three are for thesacrum 6 in order to form a triangle.

It is noted that the two-dimensional coordinates (x, y) of each pointare known in the indicator connected to the digitalized radiograph.

This first step is illustrated on each of FIGS. 1 to 8.

Second Step of the Method

The second step consists of embedding the digitalized points in theradiographs of FIGS. 4 and 5 in the radiograph of FIG. 1.

During this embedding of the digitalized points or contours, it isnecessary to adjust the scale between the radiographs and to superimposethe points defining the pelvis 4 by registration (FIG. 9).

Also, embedding of the points digitalized on the radiographs of FIGS. 7and 8 is carried out in the radiograph of FIG. 6.

The digitalized points or contours relate more particularly to thoserepresenting the pelvis 4, the vertebrae underlying the instrumentation,and the lower end instrumented vertebrae (LEV). A mapping of the scalesand an adjustment or registration of the points or contour with relationto the pelvis 4 (FIG. 10) is provided in this step of the method.

Third Stop of the Process

This step consists of a three-dimensional reconstruction of thegeometric form of the vertebrae 2 and more particularly the endinstrumented vertebrae from the sagittal (FIG. 1) and frontal (FIG. 6)radiographs, that is:

-   -   the upper end instrumented vertebrae (UEV),    -   and the lower end instrumented vertebrae (LEV).

This step also consists of determining the linear and angular geometricposition of the lower end instrumented vertebrae (LEV) reconstructedwith relation to the front and side radiographs (positioning of thepatient with relation to the films (Rx) when radiographic images aretaken).

During this step it is necessary to:represent the geometric indicators,that is:

-   -   a three-dimensional indicator is associated with the        three-dimensional geometry of the upper end instrumented        vertebrae (UEV),    -   a three-dimensional indicator is associated with the        three-dimensional geometry of the upper [sic] end instrumented        vertebrae (LEV),    -   a two-dimensional indicator is associated with the projection of        -the geometric form of the upper end instrumented vertebrae        (LEV) [sic] on the side radiograph (FIG. 1),.    -   a two-dimensional indicator is associated with the projection of        the geometric form of the upper end instrumented vertebrae (LEV)        [sic] on the front radiograph (FIG. 6).

Fourth Step of the Method

This step consists of reconstructing the geometry of the externalenvelope or contour of the upper (UEV) and lower (LEV) end instrumentedvertebrae in a three-dimensional visual space.

During this step, a second reconstruction of the surface of the neuralarch of the upper (UEV) and lower (LEV) end vertebrae is provided in athree-dimensional visual space.

Fifth Step of the Method

This step consists of projecting the upper (UEV) and lower (LEV) endinstrumented vertebrae on the front and side radiographs thanks to therelationship established between the three-dimensional andtwo-dimensional indicators defined during the third step.

This step also consists of embedding the projection of the upper (UEV)and lower (LEV) end instrumented vertebrae with relation to one anotherin the radiographs of FIGS. 9 and 10 by registration of the projectionof the lower end instrumented vertebrae (LEV) on the two positions thisvertebra occupies in the radiographs of FIGS. 9 and 10.

FIGS. 11 and 12 illustrate this step.

Sixth Step of the Method

This step consists of embedding the digitalized points or contours inthe radiograph of FIG. 11 in the radiographs of FIGS. 2 and 3 byadjusting the scale between the radiographs and registration withrelation to the upper end instrumented vertebrae (UEV).

In the same manner, the points or contours digitalized on theradiographs of FIGS. 7 and 8 are embedded in the radiograph of FIG. 12,by adjusting the scale between the radiographs and registration withrelation to the upper end instrumented vertebrae (UEV).

FIGS. 13 and 14 illustrate this step.

Seventh Step of the Method

Based on the results obtained during the previous steps, this stepconsists of:

-   -   determining and calculating the relative three-dimensional        position of the upper (UEV) and lower (LEV) end instrumented        vertebrae of the corrected spinal segment,    -   determining and calculating the position of the spinal segments        located above and below the spinal segment corrected by the        spinal instrumentation according to the relative        three-dimensional position of the upper (UEV) and lower (LEV)        end instrumented vertebrae,    -   and viewing the balance or imbalance of the vertebral column 1        in front and side projection.

It is noted that for achieving the fourth step, the latter may be, forexample, achieved from the three-dimensional emitter/sensor with atracer pen allowing the reconstruction of the external contour andsurface of the neural arch of the upper (UEV) and lower (LEV) endinstrumented vertebrae in a three-dimensional visual space.

Furthermore, the implementation of the method of the invention calls fordigital image processing techniques wherein the practical implementationis within reach of a person skilled in the art.

This implementation is achieved from an image processing system to allowthe viewing of the results and the relative position in front and sideprojection of the upper (UEV) and lower (LEV) end instrumented vertebraeof the spinal segment corrected by the spinal instrumentation.

1. A method of viewing and controlling the balance of a vertebral columnof which one spinal segment is corrected by means of conventional spinalinstrumentation, characterized in that the method consists of:determining and calculating the relative three-dimensional position ofthe upper (UEV) and lower (.LEV) end instrumented vertebrae of thespinal segment corrected through anatomical points or contoursidentified or digitalized on the radiographs of the patient to betreated, determining and calculating the position of the spinal segmentswhich are located above and below the spinal segment corrected by thespinal instrumentation, through anatomical points or contours identifiedor digitalized on the radiographs of the patient to be treated,according to the relative three-dimensional position of the upper (UEV)and lower (LEV) end instrumented vertebrae, and viewing the balance orimbalance of the vertebral column (1) in the vertical position and infront and side projection.
 2. The method of viewing and controllingaccording to claim 1, characterized in that the relativethree-dimensional position of the upper (UEV) and lower (LEV) endinstrumented vertebrae of the corrected spinal segment is obtained froma first reconstruction in a three-dimensional visual space of thegeometry of the external envelop or contour of the upper (UEV) and lower(LEV) end instrumented vertebrae and a second reconstruction in athree-dimensional visual space of the surface of the neural arch of theupper (UEV) and lower (LEV) end instrumented vertebrae.
 3. The method ofviewing and controlling according to claim 2, characterized in that thefirst and second reconstruction steps in a three-dimensional visualspace allow the relative position of the upper (UEV) and lower (LEV) endinstrumented vertebrae of the corrected spinal segment to be determinedin a three-dimensional visual space.
 4. The method of viewing andcontrolling according to claim 3, characterized in that the upper (UEV)and lower (LEV) end instrumented vertebrae of the corrected spinalsegment are projected on the front and side radiographs of the patientto be treated.
 5. The method of viewing and controlling according toclaim 3, characterized in that the front and side projection of theupper (UEV) and lower (LEV) end instrumented vertebrae of the correctedspinal segment allows the position on the front and side radiographs ofthe spinal segments located above and below the corrected spinal segmentto be determined, and to view the appearance of the reconstructedvertebral column on the front and side radiographs.
 6. The method ofviewing and controlling according to claim 1, characterized in that themethod consists of identifying or digitalizing at least four pointsdelimiting a rectangle reproducing the vertebral body for each vertebraof the vertebral column.
 7. The method of viewing and controllingaccording to claim 1, characterized in that the method consists ofidentifying or digitalizing the points that correspond to theradiological indicators utilized to define the balance of the head ofthe patient with relation to the pelvis.
 8. The method of viewing andcontrolling according to claim 7, characterized in that the methodconsists of identifying or digitalizing at least ten points for the headallowing the external contour of the head to be marked.
 9. The method ofviewing and controlling according to claim 1, characterized in that themethod consists of identifying or digitalizing at least the anatomicalpoints for the pelvis defining the center of each femoral head and thesacral plate.
 10. The method of viewing and controlling according toclaim 9, characterized in that the method consists of identifying ordigitalizing at least five points for the pelvis of which one is foreach femoral head and at least three are for the sacrum in order to forma triangle.
 11. The method of viewing and controlling according to claim1, characterized in that the method consists of embedding thedigitalized points in the radiographs of the patient.
 12. The method ofviewing and controlling according to claim 1, characterized in that themethod consists of reconstructing the geometric form of the upper (UEV)and lower (LEV) end instrumented vertebrae in three dimensions from thesagittal and frontal radiographs of the patient.
 13. The method ofviewing and controlling according to claim 1, characterized in that themethod consists of determining the linear and angular geometric positionof the reconstructed lower end instrumented vertebrae (LEV) withrelation to the front and side radiographs.
 14. The method of viewingand controlling according to claim 1, characterized in that the methodconsists of projecting the upper (UEV) and lower (LEV) end instrumentedvertebrae on the front and side radiographs.
 15. The method of viewingand controlling according to claim 1, characterized in that the methodconsists of embedding the projection of the upper (UEV) and lower (LEV)end instrumented vertebrae in the radiographs, with relation to oneanother, by registration of the projection of the lower end instrumentedvertebrae (LEV).